In servicing motor vehicles it is necessary to periodically inspect brake pads or shoes of each brake assembly to determine the degree of wear of friction linings of the assemblies. Failure to inspect the linings and allowing them to become worn could result in damage to the brake assembly. As is known, a disk brake assembly includes a disc rotor secured to a wheel of a vehicle and brake pads, which engage side surfaces of the rotor to stop rotation of the vehicle wheel. A drum brake assembly includes a drum secured to the vehicle wheel and brake shoes, which engage an inner surface of the drum to stop rotation of the vehicle wheel. In either case, the brake pads or shoes ("brake pad/shoe") are generally made up of a friction lining secured to a metal plate, with rivets for example. To avoid damage to the rotors and the drums of the brake assemblies, the brake pad/shoes must be replaced before their friction linings wear beyond a predetermined amount and allow the rivets and metal plate to gouge the rotor or drum.
Once the used brake pad/shoes are removed they can be recycled by adding a new brake lining to the metal plate. Many existing brake pad/shoes include lines painted on the sides of the friction lining to provide a visual indication of wear. The painted lines, however, increase the costs of the friction lining by adding an additional step to the manufacturing process of the lining, and may be covered by dust or removed from the lining before the lining is sufficiently worn to merit replacement.
Some existing brake assemblies include mechanical devices for indicating lining wear. U.S. Pat. No. 3,533,491 to Svenson, for example, discloses a lining wear indicator having a manually actuated brake shoe position indicator. The indicator is manually pressed against the rear of the brake shoe and acts as a ruler to indicate lining wear. This indicator, however, is difficult to retrofit, and requires a person to handle the brake assembly as opposed to just observing it. U.S. Pat. No. 4,356,897 to Urban discloses a wear indicator including pins extending from the rear of the plate. Upon depressing the brake pedal, the pins indicate how far the plate travels before the lining contacts the rotor, and thereby indirectly indicate the amount of lining wear in comparison to the amount of travel for a new lining. The wear indicator of Urban, though, is difficult to retrofit to existing or replacement brake pads, must be calibrated, and the pedal force must be consistently applied to get an accurate comparison between the lining when new and the lining when worn.
Some existing wear-indicators are audible clip devices. U.S. Pat. No. 4,037,689 to Maehara, for example, discloses a device comprising a U-shaped resilient spring having a loop portion attached to the plate and curving away from the rotor and then back towards the rotor, and a second portion extending from the loop portion towards the disc rotor. When the lining becomes worn, the second portion of the clip contacts the rotor. Since the second portion is not rigidly secured to the plate but is flexibly secured to the plate with the loop portion, the second portion vibrates when it contacts the rotor and produces an audible alarm. A disadvantage of this indicator, however, is that the second portion does not provide a reliable visual indication of lining wear since it is not rigidly connected to the plate. In addition, the loop portion extends relatively far behind the plate and, therefore, may be difficult to fit in a compact or tightly packed brake assembly. Furthermore, the loop portion is permanently fixed to the plate with a rivet or weld and is not easy to reuse or retrofit.
U.S. Pat. Nos. 4,460,067 and 4,498,559 to Katagiri et al. also disclose audible wear-indicators for brakes. The devices generally include a vibration spring having a fixing portion secured to the plate, a spring portion extending from the fixing portion in a direction away from the rotor and curved to extend towards the rotor, and a vibrating portion extending from the spring portion towards the rotor. Whereby, when the lining becomes worn, the vibrating portion of the clip contacts the rotor. Since the vibrating portion is not rigidly secured to the plate, but is flexible secured through the spring portion, the vibrating portion vibrates upon contacting the rotor to produce an audible alarm. A drawback of these indicators is that the vibrating portion does not provide a reliable visual indication of lining wear since it is not rigidly connected to the plate. In addition, the spring portion extends relatively far behind the plate and, therefore, may be difficult to fit in a compact or tightly packed brake assembly. Furthermore, a disadvantage of all audible wear-indicators is that a person has to drive the vehicle and listen for audible alarms to determine whether some or all of the brake pad/shoes need replacement. Even then it may be hard to determine which if any indicator is making the noise.
What is desired, therefore, is a brake wear-indicating device that has a simple design and is easy to use and attach to a brake pad/shoe. Preferably, the indicating device will have the ability to be retrofit to existing brake assemblies or taken off a worn brake pad/shoe and easily attached to a replacement shoe. Furthermore, the device should provide a reliable visual indication of brake wear, without requiring that a person checking the pads actually have to disassembly or even touch the brake assembly or take the vehicle for a test drive.